The present invention relates to field effect transistor microwave amplifiers for amplifying a microwave signal without using a vacuum tube. These microwave amplifiers are more often used in Doppler radar systems and more particularly still in those for Earth observation, for which efforts are made to eliminate the vacuum tubes so as to reduce the weight, the space taken up and the power consumption.
The use of transistors is known, particularly field effect transistors, for amplifying microwaves, in particular in the so-called I band, which ranges at about 10 GHz. These transistors are generally formed from gallium arsenide. They can only operate as class A amplifiers, which results in a constant and fairly high power consumption. Economy in power consumption, which might be expected by using transistors instead of vaccum tubes, is thus very much reduced, since tubes are capable of operating as class C amplifiers, with an average smaller power consumption taking into account, on the one hand, the intrinsic efficiency of class C amplifiers with respect to class A amplifiers and, on the other hand, a generally low filling rate when they are used for pulsed operation (case of radars).